Peak voltage limiter



NOV 1, 1955 T. L.. DlMoND PEAK VOLTAGE LIMITER Filed Nov. 5, 1951ATTORNEY United States Patent O f` PEAK VOLTAGE LIMITER Thomas L.Dimond, Rutherford, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationNovember 3, 1951, Serial No. 254,755

Claims. (Cl. Z50-27) This invention relates to systems for storingelectrically Y characterized items of information and particularly to amemory circuit which functions to retain items of informationelectrically characterized as momentary currents of predeterminedamplitudes.

Memory or storage circuits, in general, are well known and find numerousand diverse applications in the electrical arts. ln one type of memorycircuit electric charges representing electric values are stored forcomparatively short periods of time in condensers; the maXimum storagetime in such circuits is a function of current leakage and usually is ofthe order of seconds. Longer storage periods have been attained byorganizations of circuits and apparatus which include some form ofmechanical device such as a potentiometer or switch. Other circuitshaving retentive characteristics deal primarily with information itemsof the so-called on-oit variety or which are characterized by differentdiscrete electrical quantities or values.

It is the object of this invention to provide an improved method of andmeans for storing electrically characterized items of information.

In accordance with a particular feature of the invention a momentarycurrent of any predetermined magnitude, representing an item ofinformation, is translated into a voltage which is maintainedindefinitely at a value which is a function of the magnitude of themomentary current.

In accordance with another feature of the invention a memory circuit iscontemplated in which the information characterizing currents may be ofa continuously variable pattern as opposed to one of discrete values.

A further feature of the invention resides in the use of a storagedevice, such as is shown in my Patent No. 2,430,457 of November ll,1947, which comprises two serially joined magnetic elements, one ofwhich has pernent magnet properties and is readily susceptible tomagnetization and demagnetization and the other of which is a strip ofmaterial of high permeability which saturates sharply at low fluxdensities.

In accordance with other features, the method of operation of the memorycircuit of this invention involves magnetizing the permanent magnetelement of the storage device to an extent representative of themagnitude of the momentary current employed in chaarcterizing an item ofinformation, in order to bring the other element of the device to acondition considerably past that of magnetic saturation; subjecting theother said element of the storage device to the inuence of a source ofalternating ampere turns having an instantaneous peak value in excess ofthe effective ampere turns value of the magnetizing force employed inproducing magnetic saturation of the said other element, whereby acondition of unsaturation is produced therein; deriving a voltagecommensurate with the rate of change of iux in the said other element ofthe storage device as the peak value of the alternating ampere turnsapproaches the effective ampere turns employed to produce saturation ofthe said other element; and regulat- 2,722,603 Patented Nov. 1, 1955 ICCing the said source of alternating ampere turns in accordance with thederived voltage.

These and other features of the invention will be better understood fromthe following detailed description when read with reference to theaccompanying drawings, in which:

Fig. l is a circuit diagram of the memory circuit of this invention;

Fig. 2 is a diagram of curves showing, graphically, a value X of theeffective ampere turns in the saturable element of the storage devicedue to the permanent magnet element of the device having been subjectedto the momentary iniiuence of a direct current of predeterminedmagnitude; the alternating ampere turns A which serve to cancel theeffective ampere turns X and to produce a rate of change in the flux inthe saturable element of the storage device such that a voltagecommensurate therewith and with the extent the alternating ampere turnsapproaches the value required to render the saturable element no longersaturated is generated; and the generated voltage E2; and

Fig. 3 is a curve which is the equivalent of a B-H magnetization curvefor the permanent magnet element of the storage device.

Referring to Fig. l of the drawings the basic storage device M is acomposite core comprising two serially joined elements 24 and 2S. Theelement 24 is of a material having permanent magnet characteristics andis capable of being readily magnetized and demagnetized while theelement 25 is a strip of material which has high permeability and whichsaturates sharply at low ux densities.

The permanent magnet element 24 of the storage device is provided with awinding W1 which terminates at one end at ground potential and at theother end in the malte contacts of two switching devices 27 and 23.These switching devices may be controlled manually, electromagneticaliyor in any manner suitable to the conditions under which the memorycircuit is employed. The switching device 27 functions, when operated,to complete a connection of momentary duration between the winding Wland the positive pole of a direct-current source (not shown) by way of avariable resistance 29. The switching device 2S functions, whenoperated, to complete a circuit between the winding W1 and the negativepole of the direct-current source by way of resistance 39. When theswitch 27 is operated to closed position current traverses the windingW1 so as to effect the magnetization of the element 24 in one directionwhereas, when the switch 28 is closed current traverses the winding W1so as to magnetize the element 24 in the opposite direction.

The saturable strip 25 carries two windings W2 and W3, the former beingincluded in the plate circuit of a vacuum tube 33 and the latter beingincluded in the plate circuit of the rectifier tube 34.

The plate, grid and cathode of tube 33 and the associated biasingresistance 35 and by-pass condenser 36 constitute a simple ampliierwhose plate circuit includes the condenser 37 as well as the winding W2and whose grid, or control electrode, is connected to a source ofaiternating-current voltage 33 by way of condenser 39. Plate battery isshown at 52.

The tube 34 whose plate circuit includes the condenser 4l as well as thewinding W3, together with resistances i2 and 43 and condenser 44constitute a simple rectifier, the output voltage of which is applied tothe grid of tube 33 by way of conductor 45 and resistance 46.

The tube 4@ and its associated condensers 47 and 48 and resistances 49and 5t) constitute a second rectifier whose output voltage appears atterminal 51. rifhis output voltage is a measure of the magnitude of themomentary input current traversing the winding W1. If analternatingcurrent voltage is desired instead of a direct-currentvoltage the rectifier tube lil and its associated circuit elements maybe omitted.

ln describing the operation of the memory circuit disclosed in Fig. l,it will be assumed that the switches 27 and 2S are open and that theelement 24 of the storage device M has been partially magnetized by amomentary closure of the switch 27. The extent to which the element 24becomes magnetized depends upon the magnitude of the current whichtraverses the winding W1 but is suiicient to more than saturate theelement 2S. The magnetic saturation of the element 2S results from thefact that the magnetization of the element 24 is the equivalent of acertain number of ampere turns linking the strip 25. This value ofampere turns is herein designated X and is shown on the curve diagram ofFig. 2.

The alternating-current source 38 applies a voltage to the grid of tube33 and produces a voltage El in the plate circuit of the tube. Thisvoltage produces an alternating current in the winding W2 which producesthe alternating ampere turns represented by the curve A in Fig. 2.

The ampere turns resulting from the liow of current in the winding W2are maintained at a peak value somewhat less than the value X, or to avalue somewhat above the line B in Fig. 2 by the back biasing of thetube 33 due to the following action: As the instantaneous ampere turnsin W2, due to the voltage El, reach a value such that they cancel theeffective ampere turns X suliiciently that the strip 25 is no longersaturated, the ux in the strip 25 will change at a rate dependent on theslope of the ampere turns curve A where it enters the unsaturated rangeof strip 25, which range is indicated as confined between the lines Band C in Fig. 2. Because of this rate of change of flux in the strip 25a voltage is induced in the winding W3. This voltage is indicated by thedownward pip b on the voltage curve in Fig. 2. Assuming the ampere turnsin winding W2 start to decrease a short time later, another voltage pipshown at c is generated. On the next positive peak d of ampere turns theaction just described is repeated.

The voltage thus generated in the winding W3 is rectiied by theconventional rectiiier including tube 'el-t and appears a direct-currentvoltage E2 which is applied to the grid of tube 33 by way of conductor45 and resistance 4:6. This is the negative bias voltage for the tube 33and determines the gain of the tube.

It will now be assumed that the alternating-current voltage increases.When this occurs the current in winding WZ experiences a correspondingincrease with the result that the peak of the ampere turns, curve A, e)l further into the unsaturated range of strip 25 and because the slopeof the curve is greater in the unsaturated region and the rate of changeof ilux in the strip Z5 correspondingly greater, the resulting eakvoltages produced in the winding "t" 3 will be greater as will also thevoltage E2 which is applied to the grid of tube 33. Thus the gain oftube 33 is reduced so that the voltage El, which is the output voltageof the tube 33, remains at substantially the value it had before thealternating-current voltage increased. it is apparent therefore, thatthe voltage Ei is held to a practically constant value dependent uponthe effective ampere turns X in the strip 25 due to the element 24 ofthe storage device having been energized by the momentary closure ofswitch 27. ln other words, the alternating-current voltage El andtherefore, the direct-- current voltage E3 appearing at terminal Sli areheld at a constant value which is a function of the magnitude of thecurrent which tranversed the winding Wl of the storage device M incidentto the momentary closure of switch 27.

From the foregoing it is apparent that the tube 33 tends to seek a gainwhich makes the peak value of the ampere turns in the winding W2substantially equal to the eff tive ampere turns X produced by thewinding W1 reg less of the value of the current used in magnetizingelement 24.

The resistance 29 in Fig. l is shown to be variable indicating that anyvalue of current may be used to produce the ampere turns X. Assuming itis desirable to store an item of information which is characterized bysome other value of current and therefore, by a diierent value of ampereturns in the winding W1, it is necessary that the following procedure becarried out: Assuming it is desirable to change X from a value X1 to avalue X2 (Fig. 3), the switch 28 is operated to its closed position. Theampere turns in W1 immediately drop to the point D on the curve (Fig. 3)and the eiective ampere turns due to the magnetization drop to the pointG. The point G is beyond saturation so that it represents a startingpoint for X for various values of resistance 29. The switch 2S is thenreleased and the switch 27 closed after the resistance 29 has beenchanged to the appropriate value to produce F ampere turns in thewinding W1. Switch Z7 then is opened and the ampere turns value isestablished at X2.

While the memory circuit of this invention has many applications in theelectrical arts the following possible application is described by wayof example and involves a number of amplifiers, the output level ofwhich should be equal and of predetermined level. Each such amplifierwould obtain grid bias for its tubes from the voltage E3 in its owncircuit such as shown in Fig. l. A test circuit would measure the outputof each ampliiier, one at a time, and if the output is not the propervalue the test circuit would adjust the gain until it is. This is doneby changing the amount of magnetization in the permanent magnet element24 of the storage device. The test circuit would proceed from amplier toamplifier, setting the grid bias of each for proper gain. The grid biasremains xed between settings because of the memory action of the circuitof this invention.

What is claimed is:

1. A memory circuit comprising, in combination, a storage deviceincluding two serially joined magnetic core elements, one of which isreadily magnetizable and demagnetizable and the other of which is ofhigh permeability and saturates sharply at low flux densities, a sourceof direct current of predetermined magnitude, means for momentarilysubjecting the rst said core element to the influence of current fromsaid source to magnetize said core element to an extent representativeof the magnitude of the current from said source whereby a condition ofmagnetization which exceeds saturation is produced in the second coreelement, means including a source of alternating current for producingan alternating magnetic flux in the second core element whose peak valueis more than sufficient to cancel the saturating liux therein wherebyperiodic flux reversals are set up in said second core element, meansresponsive to the periodic flux reversals for generating voltagescommensurate with the rate of change of i'lux during the ux reversals,and means for regulating the said alternating flux producing means inaccordance with the generated voltages.

2. A memory circuit including, in combination, an electromagnetcomprising a permanent magnet core section and a serially joinedsaturable section of highly permeable material which saturates readilyat low ux densities, a winding on the permanent magnet section of saidelectromagnet, first and second windings on the saturable section ofsaid electromagnet, means for causing the winding on the permanentmagnet section to be traversed momentarily by direct current ofpredetermined magnitude whereby said permanent magnet section ismagnetized to an extent representative of the magnitude of the directcurrent and the saturable section is magnetized in excess of saturation,means including a source of alternating current and a vacuum tubeamplifier having a control electrode for applying an alternating voltageto said tirst winding on the saturable section of said electromagnetwhereby a condition of unsaturation is produced in the said saturablesection and a voltage is generated in the second winding on saidsaturable section which is commensurate with the extent to which theapplied alternating voltage exceeds that required to produce thecondition of unsaturation in saturable section, and means for regulatingthe applied alternating-current voltage in accordance with the voltagegenerated in said second winding on the said saturable section of saidelectromagnct including a connection between the said second winding ofsaid saturable section and the control electrode of said vacuum tubeamplifier.

3. A memory circuit comprising, in combination, a storage deviceincluding two serially joined magnetic elements, one of which is readilymagnetizable and demagnetizable and the other of which is of highpermeability and saturates sharply at low flux densities, a source ofdirect current of predetermined magnitude, means for momentarilysubjecting the first said core element of said storage device to theinfluence of current from said source to magnetize said first coreelement to an extent commensurate with the magnitude of said currentwhereby a condition of magnetization which exceeds saturation isproduced in the said second core element of said storage device, meansincluding a source of alternating current and a vacuum tube amplifierhaving a control electrode for producing an alternating fiux in saidsecond core element having an instantaneous peak ampere turns value inexcess of the effective ampere turns value of the saturating flux insaid second element whereby said second element becomes unsaturated andperiodic flux reversals are produced therein, means responsive to theperiodic ilux reversals for deriving a voltage commensurate with theextent to which the instantaneous peak ampere turns value of the fiuxproduced by said alternating flux producing means exceeds the effectiveampere turns of the saturating flux, and means for regulating saidalternating ux producing means in accordance with the magnitude of thederived voltage including means for subjecting the control electrode ofsaid vacuum tube amplifier to the inuence of the derived voltage.

4. In a memory circuit, in combination, a storage device comprising twoserially joined magnetic sections, the first of which is readilymagnetizable and demagnetizable and the second of which is of highpermeability and saturates sharply at low flux densities, a winding onthe said first section of said storage device, a pair of windings on thesecond section of said storage device, a source of direct current,switching means for momentarily connecting said source of direct currentto the winding on the said tirst section whereby said rst section ismagnetized to an extent representative of the magnitude of the currentfrom said source which traversed said winding and said second section ismagnetized to a condition exceeding saturation, a source of alternatingcurrent, a vacuum tube amplifier having a plate circuit which includesone of the windings on the said second section of said storage deviceand a control electrode connected to one terminal of saidalternatingcurrent source whereby the condition of magnetization of thesaid second section is altered in accordance with the peak voltageoutput of said tube and an alternating flux is generated in the saidsecond section whose rate of change varies with the extent to which thepeak value of the generated ux extends within the range of unsaturationof the second section of said storage device, means including the otherwinding on the said second section of said storage device for deriving avoltage commensurate with the said rate of change of flux in the saidsecond section, and means for applying the derived voltage to the gridelectrode of said vacuum tube to adjust the gain thereof in accordancewith the magnitude of the derived voltage.

5. In a peak voltage control circuit, a source of variable potential tobe controlled, an electromagnet comprising a permanent magnet coresection and a serially joined saturable section of highly permeablematerial and saturable at low ux densities, means for magnetizing thepermanent magnet core section of said electromagnet to a degreerepresentative of the desired peak voltage and to thereby produce insaid saturable core section a condition of magnetization considerablybeyond saturation, means including said source of variable potential forsubjecting said saturable core section to a magnetizing force such thata condition of unsaturation is produced in said saturable core sectionand the magnetic fiux therein changes at a rate commensurate with theextent to which the magnetizing force producing unsaturation extendswithin the unsaturated range of said saturable core section, means forderiving a voltage commensurate with the rate of change of flux in saidsaturable core section, and means for regulating the said magnetizingforce producing unsaturation of said saturable core element inaccordance with the derived voltage.

References Cited in the file of this patent UNITED STATES PATENTS2,430,457 Dimond Nov. 11, 1947 2,574,229 Schlesinger Nov. 6, 19512,591,406 Carter Apr. 1, 1952 FOREIGN PATENTS 487,016 Germany Nov. 30,1929 730,036 Germany Jan. 6, 1943

